Wheels spinning, tire tread searching for grip, Lee Klancher steered his motorcycle between two ruts before skidding to a stop. It was day No. 2 of the Caravana festival, a weeklong expedition held semiannually in the wilds of South America, and Klancher, a veteran rider from St. Paul, Minn., had signed up to attempt a road rarely traveled through the Amazon Basin.

“We were 200 miles from anything resembling civilization,” he said. “An all-out adventure.”

Like dozens of wilderness roads around the planet, the Caravana route—a 100-mile track in northern Bolivia—is just barely navigable with motorized transportation. But that didn’t deter the dozens of participants, including American tourists and South American dignitaries, who revved up at a remote start line to throttle north into the unknown.

Since the dawn of motorized transit, deep jungle and high mountains haven’t stopped humans from trying to lay roads through the planet’s most treacherous terrain. Some are primitive trails that evolved to accommodate four wheels and a motor, while others were forged by blasting through whatever nature put in the way.

These roads can be found all over the world. In the American West, where wagon tracks still scar sandstone in the desert, wild roads climb and dip along rivers and through canyons once used as waypoints for wilderness travel. And roads like the Karakorum Highway in Pakistan, a two-lane that climbs past 16,000 feet, have put pavement over parts of the historical Silk Route.

They’re not always in the best shape. Despite the super highways of the Western world, roads in many countries remain vastly unimproved. Sometimes they’re used by adventure travelers like Klancher. The Canning Stock Route in Western Australia, for example, attracts four-wheel-drive enthusiasts to motor in convoys for 1,100 miles in a sun-baked expanse as desolate as Mars. But, be it a public bus route in Africa or a farm-to-market track in the mountains of Mexico, the world’s most dangerous roads were built first for transit and trade.

Either way, they can be heart-stopping—and perilous to traverse. Bolivia’s North Yungas Road, an archetype of danger dubbed the “Road of Death,” is a mountain-hugging lane lined by 1,000-foot drops. Robin Esrock, a television host from Vancouver who has twice descended North Yungas on a bike, cites the jungle lane as the most dangerous road he’s seen. “It’s a winding narrow track that skirts huge drops with a near miss around every corner.”

The Halsema Highway, an unpaved mountain road in the Philippines’ Cordillera Central range, seems tailor-made for the likes of Indiana Jones. Here, foggy cloud forests and landslides could come up around any given turn.

Sometimes the risk isn’t just topographical. Mark Jenkins, a staff writer with National Geographic, hiked the Stilwell Road, from India into Burma, in 1996 while researching a book. While traversing this infamous World War II supply line, Jenkins tiptoed unauthorized into the totalitarian regime, trekking for two nights in the jungle before eventually facing a military arrest. “It’s not a road I recommend,” Jenkins said.

The following 10 roads, from Klancher’s Bolivia route to a forsaken highway in Russia, represent some of the planet’s most harrowing. Ride, drive, or hike at your own risk.